The present invention relates to a fluidized bed reactor for gas phase olefin polymerization, a process for polymerizing an olefin, and a process for producing an olefinic polymer.
Recently, productivity of an olefinic polymer has been greatly increased owing to an improvement in an activity of a transition metal catalyst for olefin polymerization. As a result, an operation for removing the catalyst residue in the produced olefinic polymer after completion of the polymerization is omitted. When using such a highly active catalyst, gas phase polymerization, which carries out an olefin polymerization in a gas phase, is generally adopted, because the gas phase polymerization is the simplest in its operation after completion of the polymerization.
For such a gas phase polymerization, a fluidized bed reactor for a gas phase polymerization is usually used to carry out the polymerization smoothly. Here, the term, xe2x80x9cfluidized bed reactor for gas phase polymerizationxe2x80x9d, means a polymerization reactor which uses a fluidized bed. In the gas phase polymerization, particles present in the reactor are subjected to reaction in their suspended state, which is formed by a gas led into the reactor through many small holes of a gas distribution plate provided to the lower part of the reactor.
Polymer powder produced in the polymerization reactor is drawn out by a pressure difference between the inside pressure and the outside pressure of the reactor, through a drawing-out means such as a drawing-out pipe provided to a side wall of the reactor. In this regard, when an amount of a gas drawn out together with the polymer powder is increased, equipment costs and operation costs for treating the gas are also increased. Thus, how to improve a polymer powder drawing-out efficiency is one of problems for designing the fluidized bed reactor. Here, the term, xe2x80x9cpolymer powder drawing-out efficiencyxe2x80x9d, means a proportion of the polymer powder contained in the reaction mixture drawn out through said drawing-out pipe. The larger the proportion, the better the efficiency.
As mentioned above, the process using a highly active catalyst in the fluidized bed reactor for a gas phase polymerization can give an olefinic polymer extremely efficiently. However, it happens occasionally that a higher temperature region is locally made at a very limited part in the fluidized bed, and as a result, the polymer powder is aggregated to form massive products. Said massive products fall on the gas distribution plate, and then stay near the reactor wall above the gas distribution plate. If the massive products are allowed to stay without drawing out from the polymerization reactor, it is highly possible that the massive products grow up to become larger massive products, or make troubles such as blocking up holes of the gas distribution plate, and thereby discontinuing the operation. Therefore, it is necessary to provide a drawing-out pipe to the reactor wall above and near the gas distribution plate to draw out the massive products together with the polymer powder.
However, there is a problem such that the olefinic polymer powder drawn out through such a drawing-out pipe is accompanied with a remarkable amount of the gas, which makes the polymer powder drawing-out efficiency inferior.
Further, when an intermittently drawing-out process, which is carried out in a manner such that a valve connected on the way of a drawing-out pipe is opened and shut at a predetermined time interval, is adopted, there is another problem such that when a time of shutting the valve is too long, the polymerization activity-carrying polymer powder, which remains in the pipe and the valve, forms massive products due to insufficient removal of heat, and thereby blocking up the pipe with the massive products.
Accordingly, an object of the present invention is to provide a fluidized bed reactor for gas phase olefin polymerization, a process for polymerizing an olefin, and a process for producing an olefinic polymer, which can draw out massive products together with the olefinic polymer powder with high efficiency.
Another object of the present invention is to provide a process for polymerizing an olefin, and a process for producing an olefinic polymer, whereby the massive products can be drawn out together with the olefinic polymer powder with high efficiency, and moreover neither any area from a polymerization reactor to a valve for drawing out the olefinic polymer powder nor the inside of the valve can be blocked up with the massive products.
The present inventors have undertaken extensive studies to create a fluidized bed reactor for gas phase olefin polymerization, which can draw out massive products together with the olefinic polymer powder with high efficiency. As a result, it has been found that the object of the present invention can be accomplished by providing at least one drawing-out means within every two specific zones of a fluidized bed reactor for polymerization, and then drawing out the olefinic polymer powder through said drawing-out means. And thereby, the present invention has been attained.
Further, the present inventors have undertaken extensive studies to create a process for polymerizing olefin, whereby the massive products can be drawn out together with the olefinic polymer powder with high efficiency, and neither any area from a polymerization reactor to a valve for drawing out the olefinic polymer powder nor the inside of the valve can be blocked up with the massive products. As a result, it has been found that the object of the present invention can be accomplished by controlling a residence time of the olefinic polymer powder inside the drawing-out means within a specific time. And thereby, the present invention has been attained.
The present invention provides a fluidized bed reactor for gas phase olefin polymerization, which has at least one drawing-out means for drawing out olefinic polymer powder within every zone of:
(i) a zone (zone X) from a gas distribution plate to a height L1 satisfying the following formula (1); and
(ii) another zone (zone Y) from a height L2 satisfying the following formula (2) to a powder level height of a fluidized bed,
L1 less than 0.1xc3x97Dxe2x80x83xe2x80x83(1)
L2=0.1xc3x97Dxe2x80x83xe2x80x83(2)
wherein L1 is a height from the gas distribution plate to an upper limit of said zone X; L2 is a height from the gas distribution plate to a lower limit of said zone Y; and D is the inside diameter of the fluidized bed reactor for gas phase polymerization, in which the olefinic polymer powder forms the fluidized bed.
The present invention also provides a process for polymerizing an olefin, which comprises the steps of (i) polymerizing an olefin in the aforesaid fluidized bed reactor for gas phase polymerization and (ii) drawing out the produced olefinic polymer powder through said drawing-out means.
The present invention further provides a process for producing an olefinic polymer, which comprises the steps of (i) polymerizing an olefin in the aforesaid fluidized bed reactor for gas phase polymerization and (ii) drawing out the produced olefinic polymer powder through said drawing-out means.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.